For routine frozens, you don't need liquid nitrogen --just a really good
source of COLD. Snap freezing is for certain things like muscle biopies--not
everything. If you don't need snap freezing, we need to know what sources
of 'cold' you do have? A -70 freezer would do it--or even slightly warmer
than this--but colder than a regular home frige. This might not be a
solution for you as it appears you're doing research--do you have some
practice tissue to see if this will work without significant artifact?
You can purchase frozen embedding molds from Surgipath and a few other
vendors. They're plastic like disposable paraffin molds and come in various
sizes. They're like a cassette without a lid and have a lip on which to
write with a sharpie or histomarker. Paraffin disposable molds will work,
but they crack and don't have as much room for writing. Put in your tissue,
surround with OCT but don't over-fill, place on the coldest horizontal
surface of the interior of your -70 and close the door. Once frozen,
transport them. Before mounting on the chuck, score the surface of the
frozen OCT so the new liquid OCT has something to grab onto. These mounts
will break off if handled too aggressively so by roughing up the surface,
the weakest union isn't the one you just created.
Let the tissue in the frozen OCT and the new 'mounting' OCT harden/freeze
and come to ambient temp in the cryostat and cut. If you cut more than one
block at a time add a little piece of paper into the side of the liquid
mounting OCT to carry the label once removed from the mold, the way we used
to before cassettes were created. Label the paper with the tissue ID
sticking out the side, if mounted in a downward position, won't get in the
way of the knife and will stay put until you thaw.
If you don't have an electrical source of cold, dry ice would work for
smaller bits--but not so well with the larger ones. And don't forget safety
with this cold stuff!! Practice a mock run before doing important tissue,
too, in case the process needs tweaking or just plain fails!
Hope this helps!
Cheryl R. Kerry, HT(ASCP)
Full Staff Inc.
Staffing the AP Lab, one great tech at a time.
800.756.3309 fax and alternate phone
[mailto:firstname.lastname@example.org] On Behalf Of Wilson,
Sent: Friday, September 28, 2007 1:28 PM
Subject: [Histonet] Flash freezing tissue for transport to be
cryostatsectioned at a later time
Hi all, How would anyone out there suggest freezing various pieces of
cat tissue to be transported to another laboratory on dry ice for
cryostat sectioning when it gets to its destination? We don't have a
cryostat or chucks on site, liquid nitrogen available. We need to be
able to keep identity of each piece. Suggestions quick please as the
necropsy team wants to stuff pieces of tissue into cryo vials and the
pieces are way to big to be stuffed and will certainly end up crushed.
Team Leader - Histology
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